This proposal is an outgrowth of studies on the modulation of HMG-CoA reductase activity in chinese hamster ovary [CHO] cells by 6-desmethyl mevinolin (ML-236B; compactin,; 6-DMM) and exogenous mevalonate. Our proposed studies are designed to characterize and define initial events in the modulation of HMG-CoA reductase activity, independently of sterol synthesis as a consequence of altered mevalonate carbon flow. I will use an established insect cell line [Kc cells derived from Drosophila embryos], which does not synthesize nor require squalene or sterol for proliferation. Non sterol isopentenoid synthesis will be modulated by mevinolin, exogenous mevalonate, or both. My studies with Kc cells will require: (a) further characterization of the spectrum of lipophilic compounds synthesized from [14C] mevalonate, (b) an assessment of the effect of mevinolin and mevalonate on selected pre- and post-HMG-CoA reductase enzymes, (c) the determination of how much mevalonate must be metabolized to suppress mevinolin enhanced HMG-CoA reductase activity, (d) the demonstration that HMG-CoA reductase suppression was related to a unique isopentenoid precursor or product, (e) the identification of the putative regulatory mevalonate product, (f) an evaluation of possible mechanisms which may define how changes in (e's) concentration result in the modulation of HMG-CoA reductase activity. It is proposed that an understanding of the regulation of Kc cell HMG-CoA reductase activity by mevalonate carbon flow may provide the added informational base needed to clearly distinguish between its modulation by sterol-independent and - dependent processes in sterologenic cells.